The invention relates to a device for picking up or displaying images having means for controlling an electron beam and at least one semiconductor device which comprises at least one semiconductor cathode, having a semiconductor body, said semiconductor body being capable of emitting electrons at a main surface of the semiconductor body from at least one region of the body in the operating condition.
Such a device is known from the Dutch Patent Application No. 7905470 of the Applicant, laid open for public inspection on Jan. 15, 1981, which corresponds to U.S. Pat. No. 4,303,930.
The invention further relates to a semiconductor device for use in such a device.
A device of the aforementioned kind may also be used, for example, in electron microscopy or electron lithography. Such a device comprises means for controlling the electron beam so that it reaches an area at which in the case of electron microscopy and electron lithography respectively a preparation to be studied and a semiconductor body, which is covered, for example, with a photolacquer, respectively, can be arranged.
However, a device for picking up images usually comprises a cathode-ray tube, which acts as a camera tube in which as a target a photosensitive layer, such as, for example, a photoconducting layer, is present. In a device for displaying images, the device generally will comprise a cathode-ray tube which acts as a display tube, while a layer or a pattern of lines or dots of a fluorescent material is provided on a target.
The use of such devices provided with semiconductor cathodes may give rise to various problems.
A first problem involves the cooling of such cathodes. This cooling is difficult due to the fact that the semiconductor bodies are located in a vacuum during operation and are moreover generally secured on lead-through pins in the end wall of a glass tube. Due to the low heat conduction of these pins and the glass, a satisfactory removal to the exterior of the energy dissipated in the cathode is prevented.
Moreover, with an increasing number of emission points, the number of lead-through pins generally increases, because it is necessary that each emission point can be controlled separately. An increase in the number of lead-through pins renders the manufacturing process more difficult, while moreover the possibility of the occurrence of leakage and hence a less satisfactory vacuum increases. This may possibly be partly avoided by constructing the control arrangement of the cathodes in the form of an integrated circuit, preferably in the same semiconductor body in which the cathode is produced. However, the dissipation of such a circuit arrangement may again impose additional requirements on the cooling of the semiconductor body, which problems have been described above.
Moreover, a quite different problem occurs with the use of several emission points, which is of an electro-optical nature. In one of the embodiments of the Dutch Patent Application No. 7905470, a semiconductor body having three semiconductor cathodes is shown, which is provided on its lower side with a conducting contact, which contacts a p-type region which is common to the three cathodes. This common contact is connected, for example, to ground, while the separate contacts are controlled by means of positive voltages at contacts, which contact n-type surface regions forming part of the separate cathodes. These voltages must be positive enough with respect to ground that avalanche multiplication occurs in the associated p-n junction and the cathode consequently emits electrons. For example, due to resistance variation in the starting material (in the present example a p-type substrate) and in contact diffusions, these voltages may greatly differ for different cathodes. Inter alia dependent upon the extent to which electron multiplication is produced, the variation in one semiconductor body may be approximately 2 Volt so that electrons are emitted from different points on one main surface, while the n-type surface at one point has a potential of, for example, approximately 6 Volt, whereas at another point this potential is approximately 8 V.
In general, after having left the cathode, the electrons in an electron-optical system first traverse an accelerating electric field, for example, due to the fact that an accelerating grid or an accelerating electrode is located at a certain distance. If now the potential of such an accelerating electrode is 20 Volt, electrons emitted by one emission point traverse a potential difference of approximately 14 Volt, whereas electrons emitted by the other emission point traverse a potential difference of approximately 12 Volt. This means that, from an electro-optical point of view, they exhibit different behavior, which is undesirable. This phenomenon will occur to a greater extent when the various emission points are distributed over several semiconductor bodies.
From an electro-optical point of view, it is therefore desirable that all emissive surfaces have substantially the same potential, which is, for example, ground potential. In the semiconductor cathodes mentioned above, this may be achieved by connecting the emissive surface regions to each other, for example, through a highly doped n-type surface zone, as the case may be in combination with a metallization pattern. For controlling the separate p-n junctions (emission points), an additional deep highly doped p-type contact zone must then be provided for each emission point at the main surface in the semiconductor body. In order to avoid excessively high series resistances and, as the case may be, mutual influencing of adjacent emission points, the semiconductor body should moreover be provided with highly doped p-type buried layers extending from the p-type contact zone to substantially under the associated p-n junction.
Apart from the disadvantages of additional processing steps (p-type contact zones and buried layers), in such a solution the problem occurs that, because it is required that each emission point can be controlled individually, the number of lead-through pins in the cathode ray tube increases with the number of emission points. This in turn gives rise to the problems already described above of maintaining the vacuum in the cathode-ray tube and the cooling of the semiconductor body, respectively.